How do I remap the 'Edit Mode' / 'Object Mode' key (tab) to a new key in Blender 2.8?
Go into Preferences > Keymap and in search type "mode"

Go down to Object Non-modal

Turn off Mode by clicking the tick

Then go to Set Object Mode

Click on tab and then press your chosen override key - 5

Make sure edit mode is selected in mode and toggle is ticked)